Machine for perforating and heat sealing a web including an elongated element with a multiplicity of drivers

ABSTRACT

Machines with elongated elements operable on an advancing web; elements such as heat seal bar, perforator blade and clamp for plastic film. Non-self supported elements are positioned and driven by drivers at middle and at ends, positioned by referencing stationary structure. Cam drivers, linear actuation, biased element positioning, angled push rod actuation and other features are shown. Slackness in web during heat sealing or supplemental indexing is produced by rotation of the normally stationary portion of a single direction clutch whose movable part is engaged with a shuttle belt. Compensation for slip and slackening also are achievable employing a differential drive between input and output nip roll pairs, with selected driving of the third shaft of the differential. Prolonged driving of the same differential can establish a desired speed ratio between the two nip pairs to compensate for slip, and change of the rotational input in response to a position sensor serves as a registry control.

United States Patent [191 Schott, Jr.

[4 1 Nov. 27, 1973 MACHINE FOR PERFORATING AND HEAT SEALING A WEBINCLUDING AN ELONGATED ELEMENT WITH A MULTIPLICITY OF DRIVERS [75]Inventor: Charles M. Schott, Jr., Gloucester,

Mass.

[73] Assignee: Gloucester Engineering Co., Inc.,

Gloucester, Mass.

22 Filed: July 6,1971

21 Appl.No.:159,993

[52] US. Cl 156/510, 83/627, 156/583 [51] Int. Cl. .i B32b 31/00, B26d5/08 [58] Field of Search 156/583, 510;

[56] References Cited UNITED STATES PATENTS 8/1966 Hanggi 83/627 2/1884l-lawley 12/1970 Schwarzkopf 156/583 Primary ExaminerDouglas J. DrummondAttorney-John Noel Williams [5 7] ABSTRACT Machines with elongatedelements operable on an advancing web; elements such as heat seal bar,perforator blade and clamp for plastic film. Non-self supported elementsare positioned and driven by drivers at middle and at ends, positionedby referencing stationary structure. Cam drivers, linear actuation,biased element positioning, angled push rod actuation and other featuresare shown. Slackness in web during heat sealing or supplemental indexingis produced by rotation of the normally stationary portion of a singledirection clutch whose movable part is engaged with a shuttle belt.Compensation for slip and slackening also are achievable employing adifferential drive between input and output nip roll pairs, withselected driving of the third shaft of the differential. Prolongeddriving of the same differential can establish a desired speed ratiobetween the two nip pairs to compensate for slip, and change of therotational input in response to a position sensor serves as a registrycontrol.

16 Claims, 11 Drawing Figures PATENTED NOV 2 7 I975 SHEET 10F 7 SHEET HE? PATENTED NOV 2 7 I973 I O l L PATENTEI] NOV 2 7 I975 SHEET 5 OF 7PATENTEUHUVZY 197s SHEET 8 [IF 7 MACHINE FOR PERFORATING AND HEATSEALING A WEB INCLUDING AN ELONGATED ELEMENT WITH A MULTIPLICITY OFDRIVERS This invention relates to machines of the type having anelongated element which periodically acts upon a web. It is particularlyrelevant to the making of long formations or imprints in plastic filmand sheet and to machines for making plastic bags.

Objects of the invention include providing such machines which arereliable and of high speed and in which the reciprocating member can bemade of any length, e.g., longer than feet, to span webs of similarwidth.

Particular objects are to provide such a machine which can act upon wideplastic webs with controllable accuracy over the entire extent of theactive element.

The invention features an elongated element or forming surface and itsassociated reciprocating assembly which lacks self-support over itslength sufficient to maintain the desired geometry of the element.Stationary structure which extends along the length of the elementallows the desired back and forth motion of the element, and amultiplicity of drivers are spaced apart along the element, at itsmiddle as well as at its ends. Each of these drivers includes adrive-force-receiving portion on the movable assembly and a drive forceapplying portion positioned by the stationary structure and mounted formovement relative to it. A main drive drives all of the force-applyingportions in synchronisrn. This movement is effective to move the elementin the predetermined direction and at the same time maintain the properposition and geometry of the element.

By use of this structure the movable element may be of low mass(permitting high speed), of simple construction and capable of simpleadjustment, e.g., to contour the element as desired.

Preferred embodiments of the invention feature: a series of individualadjustment devices along the length of the active element; thestationary structure comprising an elongated beam extending across thewidth of the web and supported on end columns; associated drive means,for the drivers, extending along the elongated beam; active elements asforming dies, specifically exampled by a plastic heat-sealing bar, asplastic penetrating means exampled by a plastic perforator and asclamping surfaces exampled by the heat seal bar as well as strippersassociated with the perforator. In the case of heat seal bars theinvention features a protective curtain means associated with the bar,in which both bar and curtain means lack self-support and are positionedby the drivers through reference to the stationary structure.

The invention features the drivers as cam assemblies; the active elementslidably guided by the stationary structure to reciprocate linearly; aseries of support columns associated with the active element; and pushrod actuation of a linkage for driving the drivers in synchronism; andboth rotary and axially operable actuators provide means for driving thepush rods and adjusting the stroke. In preferred embodiments positioningtorque is applied to the active element preferably by the same series ofsprings that provide for return movement of the active element.

These and other objects and features of the invention will be more fullyunderstood in the light of the following description of the preferredembodiments in connection with the drawings, wherein:

FIG. 1 is a perspective view, partially broken away, of a preferredembodiment of the invention useful for manufacturing plastic bags;

FIG.- 2 is a diagrammatic, partially broken away perspective view of themachine of FIG. 1 viewing the side of the heat seal bar mechanism;

FIG. 3 is a cross-sectional view of the embodiment of FIG. 1 taken online 33 thereof;

FIG. 4 is a cross-sectional view on a larger scale of portions of FIG. 3showing the heat seal bar assembly details;

FIG. 5 is a view on scale similar to FIG. 4 showing perforator bladeassembly details;

FIG. 6 is a partially diagrammatic plan view with portions broken awayof the preferred embodiment;

' FIG. 7 is a side view of one side of the machine showing in particularthe actuating arrangement for the heat seal bar FIG. 8 is a side view ofthe other side of the machine showing the actuating arrangement for theperforator blade and FIG. 9 is a diagrammatic side view of a film driveaccording to the invention while FIGS. 10 and 11 are cross-sectional,partially diagrammatic views of preferred one way clutch assemblies foraccomplishing web salackening and supplemental indexing.

Referring to the drawings, there is shown a preferred embodiment of theinvention in which polyethylene film-8 is introduced between ahorizontal heat sealing bar 10, of length L, e.g., of l0.or 10 feet, anda lower platen 12. The elongated reciprocating heat sealing bar 10 isconnected to driven column members 14 through flexures 18, all formingpart of an elongated vertically reciprocating assembly. Thereciprocating assembly is intentionally light-weight so that it mayreciprocate quickly; however the assemblyy lacks sufficient selfsupportto maintain the proper geometry of the heat sealing surface 10a alongits entire length. The column members 14 are driven at theirupper endsin the vertical direction, transverse to the length of the heat sealingbar, by reciprocating cam assemblies which are spaced apart along thelength of the heat sealing bar. Each of these comprises a first portion,cam followers 22, and a second portion, cam surfaces 24. The camsurfaces are reciprocated synchronously in the longitudinal, horizontaldirection by a plurality of connecting rods 28 in a direction parallelto the heat sealing bar, these rods interconnecting the cam surfaceswith a drive means 30, for example, a hydraulic-actuated piston. The camsurfaces are slidably positioned for this motion by verticallyadjustable extensions 31 FIG. 2 (see 68 FIG. 3) of the stationarystructure 32, which comprises a rigid beam extending across the width ofthe web, supported by end pedestals 32a. The cam assembly is-urgedtogether by the action of arms 33, connected to columns 14, and springs34; the resultant force of the springs tending to urge the cam followersagainst the respective cam surfaces. The rigidity of the stationarystructure is thus transferred to the reciprocating assembly through theadjustable extensions 31, via the cam assemblies, and eventually to thheat sealing bar through the flexures 18 which are stiff in the verticaldirection. The flexure connections are made periodically along the heatsealing bar, thus providing several points of transfer of the supportingforces.

As the second portions 24 of the driven assemblies, i.e., the camsurfaces, reciprocate in synchronism in the longitudinal direction,along the length of beam 32, the first portions 22 of the drivenassemblies, i.e., the cam followers, reciprocate in the predeterminedtransverse direction, i.e., the vertical direction, thereby causingbodily reciprocation of the columns 14, fexures 18, and heat sealing bar10. At the same time, forces transmitted by the cam surfaces serve tosupport and position adjacent portions of the bar vertically so as topreserve the desired geometry of the elongated forming surface. Theforming surface thereby reciprocates between the inoperative positionwhereby the film can be advanced and the operative position whereby theplastic film is heat sealed.

Referring more specifically to FIGS. 2, 3 and 4, the elongated heatsealing bar consists in part of an upper bar 38 and a lower bar 40extending the length of the machine and welded as as to embrace anelongated resistive heater element 42 (e.g., of tubular type) alsoextending the length of the machine. The heater element provides heatnecessary for the sealing process. Two small diameter bobbins 44, whichextend the length of the machine and which support a non-stick,heat-resistant curtain 46 (preferably part Teflon), are also supportedalong the length of the heat sealing bar. This curtain is wound aroundone bobbin, fitted around the exterior of the lower bar 40, and is thenwound around the second bobbin, and is indexed periodically, as theexposed portion of the curtain is used, in a known manner.

This assembly (i.e., the bars, bobbins and curtain) is supported atspaced apart points by individual brackets 43 connected to flexures 18.Openings 48 in these brackets provide isolation tending to prevent thestructure above the openings from heating as the heat sealing barbecomes hot.

The brackets 43, typically ten inches apart, provide the means by whichflexures l8 join the heat sealing bar to columns 14. The brackets areslotted, providing two parts, and the flexure is typically joined tothese parts by screws. The flexure is a thin piece of metal, about 0.050inch thick, the direction of thickness being arranged in thelongitudinal direction of the bar and thus allows motion by the heatsealing bar in the longitudinal direction. The flexure however has muchgreater dimensions in the vertical direction and in the other horizontaldirection, and is therefore rigid in those directions. Thus, the heatsealing bar will not distort as its temperature rises causing expansion,but rather will cause resilient deflection of the flexures in thelongitudinal direction, while remaining straight in the vertical andother horizontal directions.

The stationary structure, which supplies rigidity to the system, iscomposed of wall members welded together to provide an elongatedhorizontal tubular structure 51 extending the length of thereciprocating assembly. The column members 14 pass through periodicallyspaced openings 53, one in each of two horizontal members, and upwardlyto support cam followers 22. The column members are typically one inchcross section tubular structures and the cam followers 22 are joined tothe top ends of the column members. Torque arm brackets 33 are joined tothe column members within the tube 51 and extend horizontally. A seriesof compression springs 34 are grounded on the stationary tube wall andact upon respective torque arms 33 to supply an upward force urging thecam followers upwardly against the cam surfaces 24. The sum of allforces on the periodically spaced columns is sufficient to raise theweight of the reciprocating assembly and thus provide positive contactof all of the cam followers against the respective cam surfaces, andautomatic return of the bars to the inoperative position upondeactivating movement of the cams.

In addition to the vertical force on column members 14, there is also atorque tending to rotate the reciprocating assembly about itslongitudinal axis due to the offset of the line of action of the springs34 on arms 33. This resiliently applied torque is effective to force thecolumn members against the bearing surfaces, upper bearing surfaces 54on one side, and lower bearing surfaces 56 on the other side of eachcolumn, thus to accurately position the assembly in the sidewisedirection. The bearing surfaces typically of anti-friction material,thus slidably position the reciprocating column members for movement inthe reciprocating direction. The lower bearings are typically freefloating bearings fitting around the lower wall member 50 for the lengthof the opening cut therein. The upper bearings are positioned by dowelsnot shown.

The cam structure includes a plurality of machined, cam surfaces 24linked together by connecting rods 28 to form a chain-like serieswherein slight, self-adjusting rotation is allowed at joints 60. Eachcam surface 24 is slidably positioned against an adjustable L-shapedblock 68, FIG. 3. The L-shaped blocks slide in the vertical direction onrod which are secured to upper stationary structure 72. The spacingbetween-the upper stationary structure and the upper surface of the L-shaped blocks is individually adjusted by the screws 74 which aresecured in the tapped upper structure 72 and seat in the recesses 78 ofthe L-shaped blocks.

The action of the cam surfaces 24 against the cam followers 22 canproduce significant longitudinal forces on the reciprocating assembly.The force vector F resulting from the contact of the cam surfacesagainst the cam followers is essentially normal to the cam surfaces andtherefore has both a vertical and a horizontal component. The verticalcomponent overcomes the spring forces and produces the downward motion.The horizontal component is a longitudinal thrust force. To oppose theselongitudinal forces, dowels 58 also secure third bearing members 80(FIG. 7) which prevent longitudinal movement of columns 14 as a resultof the longitudinal thrust force.

The drive means 30, which produces the reciprocating cam motion, ispreferably a hydraulic piston arrangement positioned as shown in FIG. 7.The linear piston arrangement advantageously allows control of thedriving force necessary for proper operative positioning of the sealingprocess when the machine is not run in a fixed gap condition. Thecylinder-piston rod arrangement preferably lies in a horizontal planeand engages the driven cam 304 at a vertical height substantially equalto the height at which the connecting rods engage the cam surfaces. Inthis manner, vertical moments resulting from the driving force aresubstantially eliminated. Being at substantially the same verticalheight as the connecting rods, the driving means must be angled awayfrom the direction of motion of the cam rod chain, at an angle A, FIG.6, the angle changing slightly as the hydraulic cylinder reciprocates.

In the preferred embodiment, the piston arrangement is horizontallyarranged and consists of a hydraulic actuated cylinder 300 pivotallymounted at point 301 with drive rod 302 engaging driven cam 304 at arotatable joint 306, preferably a bearing surface of antifrictionmaterial, to permit rotation during lengthening of the cylinder andresulting relative movement of the cam surface. The bearing surfaceengaging drive rod 302 at 306 provides the reaction force to oppose thedriving force and reduces forces normal to the driving force to aminimum.

By positioning the drive rod at an angle A to the direction of cammovement, the driving force at joint 306 has a driving component 312 inthe direction of cam movement and a smaller component 314 normal toforce 312 which force 314 being opposed by reaction forces from suitablebearing surfaces.

The throw of the linear piston driving means is fixed, however theposition of the drive can be varied by adjusting screw 308 supported bystationary structure 310. Screw 308 allows the position of pivot point301 to be changed, changing the bottom position of the reciprocatingmember, allowing easy adjustment for varying thicknesses of web. Pivotpoint 302 is defined by the recess of cylinder 300 which is engaged bythe rounded end of screw 308'and remains fixed duringa series of sealingoperations.

Drive rod 302 is always under compression to engage cam surface 304 andto ensure that the cylinder continues to engage adjusting screw 308 at apivot point 301. The forces tending to urge the surface of cam 304against piston rod 302 are the upwardspring force supplied by springs34, combined with the horizontal urging force supplied by spring 62. iThe adjusting screws 74 and vertically adjustable L- shaped blocks 68allow fine vertical adjustment of an individual cam surface to allow forlocal distortions or otherwise to contour the heat seal bar as desired.While the throw of the sealing bar is fixed by the reciprocating camassemblies and the drive means, typically threeeighths inch, theextremes of the throw are locally translated The sealingbar may beshaped by these perio'dically spaced adjustments to match anydistortions inthe lower platen 12.

The upper stationary structure 72 is part of the tubular structure 51,this weldment providing sufficient rigidity for the accurate positioningand adjustment of the heat sealing bar reciprocating motion.

Referring in particular to FIGS. 3 and 5, adjacent the heat sealing baris the reciprocating perforating blade carried on plate 100. Theperforating blade assembly unlike the heat sealing bar, need not dwellat the film and therefore may be heavier than the heat sealing barbecause more time (hence slower permissible speed) is available to movethe 'blade. It reciprocates as a result of reciprocating cam action in asimilar manner as the heat sealing bar; however, periodically spacedadjustment is not necessary, an error of 0.045 inch along the length ofthe plate not being critical.

Plate 100 is biased against cam assemblies by the action of springs 102against levers 104 (FIGS. 3, 5, 6) which are distributed periodicallyalong the length of the plate 100. Cam followers 106 are attached to arigid support 108, and the cam surfaces 110 are urged against the camfollowers by the action of the spring and lever. In order to prevent thelongitudinal thrust forces resulting from the sloping cam surfaces fromaffecting the perforating plate, contact is made by a nearlyfrictionless, rolling or sliding contact, thereby minimizing thetransfer of horizontally directed forces against the perforating plateand eliminating the need for end bearings on the plate. The preferredmethod (FIG. 8) consists of rollers 114 attached to plate 100, theserollers having a very low coefficient of friction with the cam. Thus,the longitudinal thrust load is absorbed by the rigid support 108, andthe horizontal component of force on plate as a result of contact withrollers 114 is insignificant.

It is therefore not necessary to oppose longitudinal forces on theheavier perforating plate in the manner in which bearing surfaces 58opposed longitudinal forces acting on the reciprocating heat sealingassembly.

In the preferred embodiment, the cam surface driven by driving means 350(FIG. 6) is designated the master cam and is different in constructionthan the other reciprocating cams surfaces, the slave cams 110. Themaster and slave cams are connected together and substantially alignedin one direction in a chain-like series by connecting rods 352 at joints330 which allow limited rotation. As the driving means 350 forces themaster cam to the right, FIG. 8, the resulting forces from drive camfollowers 106 transmitted to the perforating plate 100 through roller114, force the perforating plate downward, overcoming the spring forceurging the perforating plate upward.

The driving means 350 is a hydraulic rotary actuator whichadvantageously has controlled acceleration. The actuator has directionalvalves which provide selfcushioning; the cushioning occurs at the twodead center positions, which are apart and correspond to the extremes oftravel of the perforating plate, and results from a small amount ofhydraulic fluid, preferably oil, which remains in the actuator chamberunable to instantly escape from the chamber at the extreme of platetravel, thereby cushioning the extremes of travel of the drive means. Itis the cushioning action which makes the rotary actuator not preferredfor the reciprocating heat sealing bar because the forces at theextremes are difficult to control.

The range of travel of the perforating plate is established by the point352 (FIG. 6) at which the drive rod 354, which engages the master cam atbearing surfaces 356, engages the oscillatory rotating drive wheel 358.The rotation-allowing joint at point 352 is preferably a self-aligningspherical roller bearing which allows rotation as the drive wheelcircularly oscillates driving the master cam in linear reciprocation.The drive wheel, shown in FIGS. 6 and 8 near, but below the right deadcenter position, where the perforating plate is in the downward verticalposition rotates downward, through has rotated less than 180, from belowthe left dead center position. The direction of rotation then reverses.Because of the cushioning effect, the exact point of reversal is notprecisely controllable; however, since this occurs at that portion ofthe circular cycle which has an almost insignificant component in thedirection of cam reciprocation, the effect is negligible.

The bottom position of the perforating plate can be adjusted by pivotingthe rotary actuator supporting structure 360 about supporting pivotpoint 362. Thumbscrew adjustment 364 threaded through rigid support 108engages the supporting structure 360 at recess 361 through compressionline 365. Thumbscrew 364 engages compression link 365 at recess 366.Compression link 365 allows for horizontal movement of supportingstructure 360 as it pivots about pivot point 362 thereby adjusting thebottoming position of the perforating plate. Adjusting screw 364 isarranged with a shear pin to provide overload protection against theperforating plate bottoming out. If the perforating plate should bottomout, thereby able to cause destructive forces to be generated by thedrive means 350, the shear pin will release, allowing supportingstructure 360 to pivot clockwise about pivot point 362 relieving andreducing the built-up forces from the rotary actuator drive.

As with the reciprocating cam surfaces for the heat sealing structure,drive rod 354 engages the master cam at substantially the same height asthe connecting rods 352; and therefore to avoid interference with thoserods, the drive means is placed at an angle B to the plane of platereciprocation. The center of rotation 363 of the driver wheel ispositioned at all times so that the driving force on the master camalways has an upward vertical component urging the master cam againstthe guides, cam followers 106.

Also similar to the cam-drive assembly for the reciprocating heatsealing assembly, a force normal to the plane of the perforating plateis generated because of the required angle B between the direction ofdrive and the direction of the cam reciprocation. This force is opposedby supported sliding bearing surfaces, preferably anti-friction slidingbearing pads.

The master cam and slave cams are preferably placed approximately everytwenty inches along the perforating plate. The connecting rods arealways in tension, tension being supplied by the pulling master cam asthe perforating plate moves downward and are held in tension by theupward urging tendency of the perforating plate against the slave camsas the plate moves upward.

Each slave cam 110 moves to the right and downward, as the master cam110' moves to the right and downward in response to the drive force, andfollowing the action of the cam surface 370 against fixed guide camfollower 106. As the perforating plate reverses its direction the upwardurging of the plate causes the slave cams to move upward and to the leftin conjunction with the action of the master cam, the connecting rodsalways being kept in tension. Uppper guide surface 374 ensures the pathwhich the slave cams traverse.

The perforating blade 120 is mounted-in the bottom of the perforatingplate 100. Referring to FIG. 5, a notch 1-22 is machined in the plate100, in which the blade is positioned. A resilient holding strip 124 isthen placed in the notch to cover and hold the blade, and strippers 126are held in place while the gib, securing the whole assembly, isfastened to the plate with fastener 129. The strippers and web grippers126 are slotted so that they may reciprocate vertically and are springloaded 130 (FIG. 8) so that in moving vertically upward the spring forcemust be overcome. Therefore, as the plate 100 lowers, the strippersfirst contact the web. The plate continues to lower as the strippersremain stationary and the blade emerges from between the strippers toperforate the web. The motion of the plate is then reversed and as theplate moves upwards, the blade retreats between the strippers and anyweb still attached to the blade is stripped from the blade by strippers126.

The web is advantageously driven periodically past the machine by ashuttle arrangement such as is shown in applicants prior U.S. Pats, No.3,322,604, 3,361,614 and 3,526,563, to which reference is made.

Referring to FIG. 9 improvements are introduced to the machine shownenabling relaxation or supplementary indexing of the web.

The forming head 500 corresponds to the heat seal and perforator machinediscussed so far. The shuttle 510 driven by cylinder 512 takes up andpays out the web and the'single direction clutch 514, with its outerrace normally stationary and its inner race engaged with timing belt520, all as explained in U.S. Pat. No. 3,526,563.

According to the present invention instead of pennanently mounting theouter race of the single direction clutch, it is mounted to rotate, anda periodically operating drive, here cylinder 540 is adapted to beactuated immediately after the heat seal bar raises. The result of thismovement is that the plastic film moves slightly, proportional to therotation of the outer race, and is thus removed from the hot jaws of theheat seal bar where it is cooled. Upon reversal of the movement of theshuttle the cylinder may be returned to its original position, thusassuring registry.

In FIG. 10 an alternate device is shown consisting of a chain drivewhich can selectively drive the outer race. A longer range of travel canbe obtained, thus to achieve a supplementary indexing effect. Forinstance the plastic heat seal can be advanced to a pair of coolingjaws.

Referring to FIG. 8 there is also provided a drive 560 for one pair ofnip rolls the second pair being driven through a differential 570. Athird input shaft 572 to the differential selectively driven by themotor 574 provides a different speed. This motor can respond to tensionsensor 576 to adjust rate of speed for slippage. By momentarily drivingthe shaft 572 at a different speed it is possible to slacken the filmbetween the nip rolls, and reversal can remove the slack.

Another means of introducing slack is to translate a pair of nip rolls(or the idler as noted in dotted lines) slightly on a periodic basis asdesired.

What is claimed is:

1. In a machine suitable for forming articles from plastic filmincluding an elongated forming surface adapted to be heated to atemperature sufficient to weld plastic film and means to move theforming surface in a predetermined path transverse to its length to anoperative position against the film, and back therefrom to aninoperative position to allow advance of the plastic film, theimprovement wherein said elongated forming surface is defined by anelongated element flexible in the direction of said path, lackingselfsupport sufficient to maintain the proper geometry of said formingsurface throughout its length, stationary structure extending along thelength of said movable element and constructed and arranged to allowsaid motion, a multiplicity of drivers spaced apart along the length ofsaid movable element, positioned at the middle as well as the endsthereof, each driver comprising a cam and roller follower combination,one of said combination comprising a drive-force-receiving portionassociated with said movable element and the other comprising acooperating drive-force-applying portion positioned by stationarystructure and movable relative thereto, each said driver adapted, uponmovement of its force-applying portion, to position and drivetherespective portion of said movable element in said predeterminedpath, and a drive means for driving all of said force-applying portionsof said drivers in synchronism to cause bodily movement of said element,said force-applying portions and said stationary structure adapted totransmit positioning forces through said drivers sufficient to maintainsaid geometry of said forming surface during'its movement, andindividual adjustment devices associated with individual drivers, eachadjustment device adapted to permit adjustment of the position of thecorresponding portion of said elongated element in the direction oftravel relative to other portions of said elongated element.

2.- The machine of claim 1 wherein the drive-forceapplying portion ofsaid cam and roller-follower drivers are pivotally linked together in anelongated linkage extending parallel to said elongated forming surface,each said portion being free to be displaced relative to the others bythe respective adjustment device, and a reciprocating drive moving saidlinkage axially to drive and allow return of said forming surface.

3. The machine of claim 1 wherein said elongated element comprises aheat seal bar, a series of support columns spaced apart along the lengthof said bar are joined thereto through sheet-form flexures flexible onlyin the direction of the length of said bar, each column carrying thereonsaid drive-force-receiving portion of a respective cam androller-follower combination.

4. In a machine for perforating plastic film in which an elongatedplastic perforator element having a desired geometry along its lengthperiodically moves in a predetennined path transverse to said length,the element adapted to move against a web to act thereupon and away toallow web advance, said element associated with strippers movablerelative thereto during perforating and withdrawal motions, theimprovement wherein said elongated element is comprised of a series ofsegments joined together, end to end and is flexible lackingself-support sufficient to maintain said desired geometry, stationarystructure extending along the length of said movable perforator elementand constructed and arranged to allow said motion, a multiplicity ofdrivers spaced apart along the length of said movable element positionedat the middle as well as at the ends thereof, each driver comprising acam and roller follower combination, one of said combination comprisinga drive-force-receiving portion associated with said movable element andthe other comprising a cooperating drive-force-applying portionpositioned by stationary structure and movable relative thereto, eachsaid driver adapted, upon movement of its forceapplying portion, toposition and drive the respective portion of said movable element insaid predetermined path, and a drive means for driving all of saidforceapplying portions of said drivers in synchronism to cause bodilymovement of said element, said forceapplying portions and saidstationary structure adapted.

, adapted to be heated to a'temperature sufficient to weld plastic filmand means to move the forming surface in a predetermined path transverseto its length to an operative position against the film, and backtherefrom to an inoperative position to allow advance of the plasticfilm, the improvement wherein said elongated forming surface is definedby an elongated element flexible in the direction of said path, lackingselfsupport sufficient to maintain the proper geometry of said formingsurface throughout its length, stationary structure extending along thelength of said movable element and constructed and arranged to allowsaid motion, a multiplicity of drivers spaced apart along the length ofsaid movable element, positioned at the middle as well as the endsthereof, each driver comprising a drive-force-receiving portionassociated with said movable element and a cooperatingdrive-forceapplying portion positioned by stationary structure andmovable relative thereto, each said driver adapted, upon movement of itsforce-applying portion, to position and drive the respective portion ofsaid movable element in said predetermined path, and a drive means fordriving all of said force-applying portions of said drivers insynchronism to cause bodily movement of said element, saidforce-applying portions and said stationary structure adapted totransmit positioning forces through said drivers sufficient to maintainsaid geometry of said forming surface during its movement, and whereinsaid element comprises a heat seal bar and ourtain means associated withsaid bar, adapted to interpose a protective curtain between said heatseal bar and said plastic, both said heat seal bar and said curtainmeans being flexible in the direction of said path and individualadjustment devices associated with individual drivers, each adjustmentdevice adapted to permit adjustment of the position of the correspondingportion of said heat seal bar and curtain to the other portions of saidheat seal bar and curtain.

6; The machine of claim 5 wherein the drive-forceapplying portions ofsaid drivers are pivotally linked together in an elongated linkageextending parallel to said elongated forming surface, each saidportionbeing free to be displaced relative to the others by therespective adjustment device, and a reciprocating drive moving saidlinkage axially to drive and allow return of said forming surface.

7. The machine of claim 5 wherein a series of support columns spacedapart along the length of said elongated heat sealing bar and associatedcurtain means are joined thereto through flexures flexible only in thedirection of the length of said heat seal bar, each column associatedwith a respective driver for transmitting drive and positioning forcesto said heat seal bar and curtain means.

8. In a machine in which an elongated element having a desired geometryalong its length periodically moves in a predetermined path. transverseto said length, the element adapted to move against a web to actthereupon and away to allow web advance; the improvement wherein saidelongated element is flexible in the direction of said path lackingself-support sufficient to maintain said desired geometry, stationarystructure extending along the length of said movable element andconstructed and arranged to allow said motion, a multiplicity of driversspaced apart along the length of said movable element positioned at themiddle as well as at the ends thereof, each driver comprising adrive-forcereceiving portion associated with said movable element and acooperating drive-force-applying portion positioned by stationarystructure and movable relative thereto, each said driver adapted, uponmovement of its force-applying portion, to position and drive therespective portion of said movable element in said predetermined path,and a drive means for driving all of said force-applying portions ofsaid drivers in synchronism to cause bodily movement of said element,said forceapplying portions and said stationary structure adapted totransmit positioning forces through said drivers sufficient to maintainsaid desired geometry of said elongated element during its movement,

said machine adapted to operate across the width of an elongatedtraveling web, said stationary structure comprising an elongated beamstructure, stationary during operation, supported on end columns andextending across the width of said web, and said machine including thecombination of at least two elongated elements of the character abovedescribed, one of said elements comprising a heat seal bar and the othercomprising a perforator blade, each element having associated therewithan independent drive means, each of said elements positioned by itsdrivers relative to said elongated beam structure. 9. In a machine inwhich an elongated element having a desired geometry along its lengthperiodically moves in a predetermined path transverse to said length,the element adapted to move against a web to act thereupon and away toallow web advance, the improvement wherein said elongated element isflexi ble in the direction of said path lacking self-support sufficientto maintain said desired geometry, stationary structure extending alongthe length of said movable element and constructed and arranged to allowsaid motion, a multiplicity of drivers spaced apart along the length ofsaid movable element positioned at the middle as well as at the endsthereof, each driver comprising a drive-forcereceiving portionassociated with said movable element and a cooperatingdrive-force-applying portion positioned by stationary structure andmovable relative thereto, each said driver adapted, upon movement of itsforce-applying portion, to position and drive the respective portion ofsaid movable element in said predetermined path, and a drive insynchronism to cause bodily movement of said element, saidforce-applying portions and said stationary structure adapted totransmit positioning forces through said drivers sufficient to maintainsaid desired geometry of said elongated element during its movement, and

wherein said drivers comprise cam assemblies one of said portions ofeach assembly comprising a cam follower and the other of said portionscomprising a cam surface engaged with said follower, and said camassemblies are mutually driven by a linkage reciprocating in thedirection parallel to the elongated element, the machine includingresilient biasing means for resiliently urging said cam followers andcam surfaces together, said biasing means applying a torque tending torotate said elongated element about its longitudinal axis, and saidstationary structure includes bearing surfaces opposing said tendency torotate, thereby cooperating to position said element, said biasing meanscomprising a series of springs, one end of each mounted to saidstationary structure and the other end of each being positioned to applya portion of said torque, there being a series of slidable supportsspaced apart along the length of and movable with said movable element,each extending from said element to a said driver, each supportincluding a torque arm extending sideways and each said spring engaginga said torque arm.

10. The machine of claim 9 wherein said element in cludes a heat sealingbar.

11. The machine of claim 10 wherein said element includes two spacedapart bobbins, and a curtain of heat resistant, non-adherent materialextends between said bobbins under said heat sealing bar.

12. A plastic film-working machine having a pair of elongatedplastic-working elements disposed side by side in proximity, each ofsaid elements having a desired geometry along its length and movable ina predetermined path transverse to said length, each element adapted tomove against a web to act thereupon and away to allow web advance, eachsaid elongated element is flexible in the direction of said path lackingself-support sufficient to maintain said desired geometry, stationarystructure extending along the length of each said movable element andconstructed and arranged to allow said motion,'each of said elementshaving a multiplicity of drivers spaced apart along the length of thesaid movable element positioned at the middle as well as at the endsthereof, each driver comprising a cam and roller-follower combinationhaving a drive-force-receiving portion assocated with the said movableelement and a cooperating drive-forceapplying portion positioned bystationary structure and movable realtive thereto, each said driveradapted, upon movement of its force-applying portion, to position anddrive the respective portion of said movable element in saidpredetermined path, and each of said element having a separate drivemeans for driving all of said force-applying portions of the respectiveset of drivers in synchronism to cause bodily movement of the respectiveelement, said force-applying portions and said stationary structureadapted to transmit positioning forces through said drivers sufficientto maintain said desired geometry of the respective elongated elementduring it movement.

13. In a machine for forming bags from plastic film including anelongated forming surface adapted to be heated to a temperaturesufficient to weld superposed plastic films together and means to movethe forming surface in apredetermined path transverse to its length toan operative position against the film, and back therefrom to aninoperative position to allow advance of the plastic film, theimprovement wherein said elongated forrning surface is defined by anelongated element flexible in the direction of said path, lackingselfsupport sufficient to maintain the proper geometry of said formingsurface throughout its length, stationary structure extending along thelength of said movable element and constructed and arranged to allowsaid motion, a multiplicity of drivers spaced apart along the length ofsaid movable element, positioned at the middle as well as the endsthereof, each driver comprising a drive-force-receiving portionassociated with said movable element and a cooperatingdrive-forceapplying portion positioned by stationary structure andmovable relative thereto, each said driver adapted, upon movement of itsforce-applying portion, to position and drive the respective portion ofsaid movable element in said predetermined path, and a drive means fordriving all of said force-applying portions of said drivers insynchronism to cause bodily movement of said element, saidforce-applying portions and said stationary structure adapted totransmit positioning forces through said drivers sufficient to maintainsaid geometry of said forming surfaces druing its movement,

said drivers comprising cam assemblies, one of said portions of eachassembly comprising a cam follower and the other of said portionscomprising a cam surface engaged with said follower, said cam assembliesare mutually driven by a linkage reciprocating in the direction parallelto the elongated element, said linkage including movable portions ofsaid cam assemblies is biased to one position and a push rod andactuator assembly is mounted alongside said linkage at an acute anglethereto, said push rod engaged with said linkage and adapted uponactivation of said actuator to push said linkage in the directionovercoming said biasing means, I

said actuator being a fluid drive cylinder pivotally mounted at a pivotpoint fixed during operation, said rod engaging the linkage to permitrotation during lenghtening of the cylinder with the attendant change inangle between the push rod and the line of action of said linkage.

14. The machine of claim 13 wherein said pivot point is formed by anadjustable member engaging said cylinder, thereby to change the positionof said pivot point and alter the bottom position of the movableelement.

15. In a machine for forming bags from plastic film including anelongated forming surface adapted to be heated to a temperaturesufficient to weld superposed palstic films together and means to movethe forming surface in a predetermined path transverse to its length toan operative position against the film, and back therefrom to aninoperative position to allow advance of the plastic film, theimprovement wherein said elongated forming surface is defined by anelongated element flexible in the direction of said path, lackingselfsupport sufficient to maintain the proper geometry of said formingsurface throughout its length, stationary structure extending along thelength of said movable element and constructed and arranged to allowsaid motion, a multiplicity of drivers spaced apart along the length ofsaid movable element, positioned at the middle as well as the endsthereof, each driver comprising a drive-force-receiving portionassociated with said movable element and a cooperating drive-forceapplying portion positioned by stationary structure nd movable relative'thereto, each said driver adapted, upon movement of its force-applyingportion, to position and drive the respective portion of said movableelement in said predetermined path, and a drive means for driving all ofsaid force-applying portions of said drivers in synchronism to causebodily movement of said element, said force-applying portions and saidstationary structure adapted to transmit positioning forces through saiddrivers sufficient to maintain said geometry of said forming surfacedruing its movement,

said drivers comprising cam assemblies, one of said portions of eachassembly comprising a cam follower and the other of said portionscomprising a cam surface engaged with said follower, said cam assembliesare mutually driven by a linkage follower, said cam assemblies aremutually driven by a linkage reciprocating in the direction parallel tothe elongated element, said linkage including movable portions of saidcam assemblies is biased to one position and a push rod and actuatorassembly is mounted alongside said linkage at an acute angle thereto,said push rod engaged with said linkage and adapted upon activation ofsaid actuator to push said linkage in the direction overcoming saidbiasing means,

said actuator being a fluid rotary actuator, said actuator mounted onsupprting structure and said rod engaging said linkage and the rotaryactuator through rotary joints to permit an attendant change in anglerelative thereto during rotation of said actuator and reciprocation ofsaid linkage.

16. The machine of claim 15 wherein said supporting structure ispivotally mounted to permit a change in the bottoming position of saidelement and said position is adjustable by rotating said structure inthe direction of cam reciprocation by means of a supported adjustmentmember.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 s Z25Dated November 2 7 973 Invent Charles M. Schott. Jr,

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Co1. 2, line 32, "10" (second occurrence) should be --20--;

Col. line 19, "as" (first occurrence) should be --so--;

Col. line 45, "352" should be -35l--;

C01. 6, line 48, "352" should be --351--;

Col. 6, lines El and 5S, "throughhas rotated", should be has rotatedthrough;

Col. 6, line 67, "line" should be -link-;

Col. 8, line 26, "Fig. 10" should be Fig. l1-;

Col.ll, line 43, after "drive", insert means for driving all of saidforce-applying portions of said drivers- Col. 1 line 24, "lengthening"is misspelled; Col l line .34, "81861116" is misspelled; Col. 1 6 "nline should be and-;

Col. 14, lines 21-23, delete "follower, said cam assemblies are mutuallydriven by a linkage"; Co1.l4, line 33, "supporting" is misspelled.

, line 16, "during" is misspelled; v

Signed and sealed this 23rd da; of April 197 (SEAL) Attest:

EDE'IARD l-lFLLET"JHSR,Jlla C MARSHALL DANN Attesting OfficerCommissioner of Patents

1. In a macHine suitable for forming articles from plastic film including an elongated forming surface adapted to be heated to a temperature sufficient to weld plastic film and means to move the forming surface in a predetermined path transverse to its length to an operative position against the film, and back therefrom to an inoperative position to allow advance of the plastic film, the improvement wherein said elongated forming surface is defined by an elongated element flexible in the direction of said path, lacking self-support sufficient to maintain the proper geometry of said forming surface throughout its length, stationary structure extending along the length of said movable element and constructed and arranged to allow said motion, a multiplicity of drivers spaced apart along the length of said movable element, positioned at the middle as well as the ends thereof, each driver comprising a cam and roller follower combination, one of said combination comprising a drive-force-receiving portion associated with said movable element and the other comprising a cooperating drive-force-applying portion positioned by stationary structure and movable relative thereto, each said driver adapted, upon movement of its force-applying portion, to position and drive the respective portion of said movable element in said predetermined path, and a drive means for driving all of said force-applying portions of said drivers in synchronism to cause bodily movement of said element, said force-applying portions and said stationary structure adapted to transmit positioning forces through said drivers sufficient to maintain said geometry of said forming surface during its movement, and individual adjustment devices associated with individual drivers, each adjustment device adapted to permit adjustment of the position of the corresponding portion of said elongated element in the direction of travel relative to other portions of said elongated element.
 2. The machine of claim 1 wherein the drive-force-applying portion of said cam and roller-follower drivers are pivotally linked together in an elongated linkage extending parallel to said elongated forming surface, each said portion being free to be displaced relative to the others by the respective adjustment device, and a reciprocating drive moving said linkage axially to drive and allow return of said forming surface.
 3. The machine of claim 1 wherein said elongated element comprises a heat seal bar, a series of support columns spaced apart along the length of said bar are joined thereto through sheet-form flexures flexible only in the direction of the length of said bar, each column carrying thereon said drive-force-receiving portion of a respective cam and roller-follower combination.
 4. In a machine for perforating plastic film in which an elongated plastic perforator element having a desired geometry along its length periodically moves in a predetermined path transverse to said length, the element adapted to move against a web to act thereupon and away to allow web advance, said element associated with strippers movable relative thereto during perforating and withdrawal motions, the improvement wherein said elongated element is comprised of a series of segments joined together, end to end and is flexible lacking self-support sufficient to maintain said desired geometry, stationary structure extending along the length of said movable perforator element and constructed and arranged to allow said motion, a multiplicity of drivers spaced apart along the length of said movable element positioned at the middle as well as at the ends thereof, each driver comprising a cam and roller follower combination, one of said combination comprising a drive-force-receiving portion associated with said movable element and the other comprising a cooperating drive-force-applying portion positioned by stationary structure and movable relative thereto, each said driver adapted, upon movement of its force-applying portion, to position and drive the respective portion of saId movable element in said predetermined path, and a drive means for driving all of said force-applying portions of said drivers in synchronism to cause bodily movement of said element, said force-applying portions and said stationary structure adapted to transmit positioning forces through said drivers sufficient to maintain said desired geometry of said elongated element during its movement.
 5. In a machine suitable for forming articles from plastic film including an elongated forming surface adapted to be heated to a temperature sufficient to weld plastic film and means to move the forming surface in a predetermined path transverse to its length to an operative position against the film, and back therefrom to an inoperative position to allow advance of the plastic film, the improvement wherein said elongated forming surface is defined by an elongated element flexible in the direction of said path, lacking self-support sufficient to maintain the proper geometry of said forming surface throughout its length, stationary structure extending along the length of said movable element and constructed and arranged to allow said motion, a multiplicity of drivers spaced apart along the length of said movable element, positioned at the middle as well as the ends thereof, each driver comprising a drive-force-receiving portion associated with said movable element and a cooperating drive-force-applying portion positioned by stationary structure and movable relative thereto, each said driver adapted, upon movement of its force-applying portion, to position and drive the respective portion of said movable element in said predetermined path, and a drive means for driving all of said force-applying portions of said drivers in synchronism to cause bodily movement of said element, said force-applying portions and said stationary structure adapted to transmit positioning forces through said drivers sufficient to maintain said geometry of said forming surface during its movement, and wherein said element comprises a heat seal bar and curtain means associated with said bar, adapted to interpose a protective curtain between said heat seal bar and said plastic, both said heat seal bar and said curtain means being flexible in the direction of said path and individual adjustment devices associated with individual drivers, each adjustment device adapted to permit adjustment of the position of the corresponding portion of said heat seal bar and curtain to the other portions of said heat seal bar and curtain.
 6. The machine of claim 5 wherein the drive-force-applying portions of said drivers are pivotally linked together in an elongated linkage extending parallel to said elongated forming surface, each said portion being free to be displaced relative to the others by the respective adjustment device, and a reciprocating drive moving said linkage axially to drive and allow return of said forming surface.
 7. The machine of claim 5 wherein a series of support columns spaced apart along the length of said elongated heat sealing bar and associated curtain means are joined thereto through flexures flexible only in the direction of the length of said heat seal bar, each column associated with a respective driver for transmitting drive and positioning forces to said heat seal bar and curtain means.
 8. In a machine in which an elongated element having a desired geometry along its length periodically moves in a predetermined path transverse to said length, the element adapted to move against a web to act thereupon and away to allow web advance; the improvement wherein said elongated element is flexible in the direction of said path lacking self-support sufficient to maintain said desired geometry, stationary structure extending along the length of said movable element and constructed and arranged to allow said motion, a multiplicity of drivers spaced apart along the length of said movable element positioned at the middle as well as at the ends thereof, each driver comprising a drive-force-receIving portion associated with said movable element and a cooperating drive-force-applying portion positioned by stationary structure and movable relative thereto, each said driver adapted, upon movement of its force-applying portion, to position and drive the respective portion of said movable element in said predetermined path, and a drive means for driving all of said force-applying portions of said drivers in synchronism to cause bodily movement of said element, said force-applying portions and said stationary structure adapted to transmit positioning forces through said drivers sufficient to maintain said desired geometry of said elongated element during its movement, said machine adapted to operate across the width of an elongated traveling web, said stationary structure comprising an elongated beam structure, stationary during operation, supported on end columns and extending across the width of said web, and said machine including the combination of at least two elongated elements of the character above described, one of said elements comprising a heat seal bar and the other comprising a perforator blade, each element having associated therewith an independent drive means, each of said elements positioned by its drivers relative to said elongated beam structure.
 9. In a machine in which an elongated element having a desired geometry along its length periodically moves in a predetermined path transverse to said length, the element adapted to move against a web to act thereupon and away to allow web advance, the improvement wherein said elongated element is flexi ble in the direction of said path lacking self-support sufficient to maintain said desired geometry, stationary structure extending along the length of said movable element and constructed and arranged to allow said motion, a multiplicity of drivers spaced apart along the length of said movable element positioned at the middle as well as at the ends thereof, each driver comprising a drive-force-receiving portion associated with said movable element and a cooperating drive-force-applying portion positioned by stationary structure and movable relative thereto, each said driver adapted, upon movement of its force-applying portion, to position and drive the respective portion of said movable element in said predetermined path, and a drive in synchronism to cause bodily movement of said element, said force-applying portions and said stationary structure adapted to transmit positioning forces through said drivers sufficient to maintain said desired geometry of said elongated element during its movement, and wherein said drivers comprise cam assemblies one of said portions of each assembly comprising a cam follower and the other of said portions comprising a cam surface engaged with said follower, and said cam assemblies are mutually driven by a linkage reciprocating in the direction parallel to the elongated element, the machine including resilient biasing means for resiliently urging said cam followers and cam surfaces together, said biasing means applying a torque tending to rotate said elongated element about its longitudinal axis, and said stationary structure includes bearing surfaces opposing said tendency to rotate, thereby cooperating to position said element, said biasing means comprising a series of springs, one end of each mounted to said stationary structure and the other end of each being positioned to apply a portion of said torque, there being a series of slidable supports spaced apart along the length of and movable with said movable element, each extending from said element to a said driver, each support including a torque arm extending sideways and each said spring engaging a said torque arm.
 10. The machine of claim 9 wherein said element includes a heat sealing bar.
 11. The machine of claim 10 wherein said element includes two spaced apart bobbins, and a curtain of heat resistant, non-adherent material extends between said bobbins under said heat sealing bar.
 12. A plastic film-working machine having a pair of elongated plastic-working elements disposed side by side in proximity, each of said elements having a desired geometry along its length and movable in a predetermined path transverse to said length, each element adapted to move against a web to act thereupon and away to allow web advance, each said elongated element is flexible in the direction of said path lacking self-support sufficient to maintain said desired geometry, stationary structure extending along the length of each said movable element and constructed and arranged to allow said motion, each of said elements having a multiplicity of drivers spaced apart along the length of the said movable element positioned at the middle as well as at the ends thereof, each driver comprising a cam and roller-follower combination having a drive-force-receiving portion assocated with the said movable element and a cooperating drive-force-applying portion positioned by stationary structure and movable realtive thereto, each said driver adapted, upon movement of its force-applying portion, to position and drive the respective portion of said movable element in said predetermined path, and each of said element having a separate drive means for driving all of said force-applying portions of the respective set of drivers in synchronism to cause bodily movement of the respective element, said force-applying portions and said stationary structure adapted to transmit positioning forces through said drivers sufficient to maintain said desired geometry of the respective elongated element during it movement.
 13. In a machine for forming bags from plastic film including an elongated forming surface adapted to be heated to a temperature sufficient to weld superposed plastic films together and means to move the forming surface in a predetermined path transverse to its length to an operative position against the film, and back therefrom to an inoperative position to allow advance of the plastic film, the improvement wherein said elongated forming surface is defined by an elongated element flexible in the direction of said path, lacking self-support sufficient to maintain the proper geometry of said forming surface throughout its length, stationary structure extending along the length of said movable element and constructed and arranged to allow said motion, a multiplicity of drivers spaced apart along the length of said movable element, positioned at the middle as well as the ends thereof, each driver comprising a drive-force-receiving portion associated with said movable element and a cooperating drive-force-applying portion positioned by stationary structure and movable relative thereto, each said driver adapted, upon movement of its force-applying portion, to position and drive the respective portion of said movable element in said predetermined path, and a drive means for driving all of said force-applying portions of said drivers in synchronism to cause bodily movement of said element, said force-applying portions and said stationary structure adapted to transmit positioning forces through said drivers sufficient to maintain said geometry of said forming surfaces druing its movement, said drivers comprising cam assemblies, one of said portions of each assembly comprising a cam follower and the other of said portions comprising a cam surface engaged with said follower, said cam assemblies are mutually driven by a linkage reciprocating in the direction parallel to the elongated element, said linkage including movable portions of said cam assemblies is biased to one position and a push rod and actuator assembly is mounted alongside said linkage at an acute angle thereto, said push rod engaged with said linkage and adapted upon activation of said actuator to push said linkage in the direction overcoming said biasing means, said actuator being a fluid drive cylinder pivotally mounted at a pivot point fixed during operation, said rod engaging the linkage to permit rotation During lenghtening of the cylinder with the attendant change in angle between the push rod and the line of action of said linkage.
 14. The machine of claim 13 wherein said pivot point is formed by an adjustable member engaging said cylinder, thereby to change the position of said pivot point and alter the bottom position of the movable element.
 15. In a machine for forming bags from plastic film including an elongated forming surface adapted to be heated to a temperature sufficient to weld superposed palstic films together and means to move the forming surface in a predetermined path transverse to its length to an operative position against the film, and back therefrom to an inoperative position to allow advance of the plastic film, the improvement wherein said elongated forming surface is defined by an elongated element flexible in the direction of said path, lacking self-support sufficient to maintain the proper geometry of said forming surface throughout its length, stationary structure extending along the length of said movable element and constructed and arranged to allow said motion, a multiplicity of drivers spaced apart along the length of said movable element, positioned at the middle as well as the ends thereof, each driver comprising a drive-force-receiving portion associated with said movable element and a cooperating drive-force applying portion positioned by stationary structure nd movable relative thereto, each said driver adapted, upon movement of its force-applying portion, to position and drive the respective portion of said movable element in said predetermined path, and a drive means for driving all of said force-applying portions of said drivers in synchronism to cause bodily movement of said element, said force-applying portions and said stationary structure adapted to transmit positioning forces through said drivers sufficient to maintain said geometry of said forming surface druing its movement, said drivers comprising cam assemblies, one of said portions of each assembly comprising a cam follower and the other of said portions comprising a cam surface engaged with said follower, said cam assemblies are mutually driven by a linkage follower, said cam assemblies are mutually driven by a linkage reciprocating in the direction parallel to the elongated element, said linkage including movable portions of said cam assemblies is biased to one position and a push rod and actuator assembly is mounted alongside said linkage at an acute angle thereto, said push rod engaged with said linkage and adapted upon activation of said actuator to push said linkage in the direction overcoming said biasing means, said actuator being a fluid rotary actuator, said actuator mounted on supprting structure and said rod engaging said linkage and the rotary actuator through rotary joints to permit an attendant change in angle relative thereto during rotation of said actuator and reciprocation of said linkage.
 16. The machine of claim 15 wherein said supporting structure is pivotally mounted to permit a change in the bottoming position of said element and said position is adjustable by rotating said structure in the direction of cam reciprocation by means of a supported adjustment member. 